Abstract: The current generation of ultrahigh temperature ceramic precursors typically encounters obstacles in achieving high ceramic yields (<40 wt.%) due to the challenges in integrating significant amounts of boron, which hampers their conversion into boride-based ultrahigh temperature ceramics. To tackle these challenges, a serious of pioneering liquid multi-component hafnium-containing ceramic SiHfCB precursors (with different Hf/Si ratios) have been developed. These novel precursors are featured with stable molec-ular structure and high ceramic yield which were successfully created through a novel one-pot polymer-ization process. They present in liquid form and their structure is characterized by C-C bonds forming its main chain with branched chains of O-Si-O, Si-O-Hf, Si-O-B, and B-O-Hf which have untapped advantages including uniform component dispersion, and excellent fluidity. The ceramic yield of SiHfCB precursor with Hf/Si of 0.2 is remarkably up to 68.6 wt.% at 1500 ℃, and their Hf content exceeded 50 wt.%. Of particular interest, the pyrolyzed product HfB₂-SiC nanopowders derived from the SiHfCB precursor with Hf/Si of 0.2, consist of nanopowders in the 40-60 nm range with a density of 5.23 g cm^-3. Remarkably, this material demonstrates exceptional performance in ultrahigh temperature oxygen-containing environ-ments at 2500 ℃, showing near-zero ablation with a linear ablation rate of just 2.5 × 10^-4 mm s^-1. Post-ablation analysis of the microstructure reveals that the formation of a lava-like HfO₂ and HfO₂-SiO₂ oxide layer effectively blocks oxygen penetration and provides excellent oxidation resistance. The inno-vative SiHfCB hafnium-containing ceramic precursor offers a groundbreaking solution for the preparation of lightweight ultrahigh-temperature ceramics. This development is poised to provide robust technical support for the use of ultrahigh temperature ceramics in non-ablative thermal protective systems, partic-ularly in the construction of hypersonic vehicles, where ultrahigh temperature resilience is crucial.

Key words: Polymer-derived ceramics, Ultrahigh temperature ceramics precursor, Ablation resistance, Ablation mechanism